The present invention is directed to sealed power distribution modules. The invention is particularly applicable to environmentally sealed power distribution modules for use in automotive applications.
Power distribution modules, or central electric boxes, are commonly used in automotive applications to distribute power throughout an automobile. Often, circuitry is disposed on a printed circuit board which includes electrical components and tab and receptacle contacts for connection to wiring harnesses, fuses, relays and engine control units. The printed circuit board is typically disposed in a housing with a cover secured over the electrical components and terminals. The entire power distribution module is then mounted in an accessible region of the automobile, often along the bulkhead of the passenger compartment, to allow for replacement of fuses and other components and for easy performance of diagnostic tests.
Since most power distribution modules are located in the passenger compartment of an automobile, sealing the module from the environment has not been a necessity. Even for applications where a power distribution module is placed within the engine compartment of an automobile, typically only a basic cover is needed to safeguard against dirt and occasional splashing of liquids against the module. However, some more rigorous automotive applications demand reliable sealing of the power distribution module when the module is located in the engine compartment of the automobile. Such applications are dictated when continuous exposure to environmental elements is expected or if, for example, the automobile is expected to be subjected to high pressure under-carriage cleaning processes. Such is the case with many corporate fleet automobiles and commercial trucking lines.
Unfortunately, environmentally sealed housings do not present a friendly atmosphere for printed circuit boards carrying electronic components and power distribution circuitry. A sealed housing typically retains heat which leads to pressure and temperature differentials between the interior and exterior of the housing and also presents the potential for accumulation of condensation within the sealed housing. Power distribution modules generate relatively high temperatures due to the large currents being carried by the circuitry in the modules and the presence of electrical components which produce heat. The temperature and pressure differentials stress the circuit board and may cause damage to the power distribution module. Accordingly, power distribution modules have an increased sensitivity to sealed environments because of the rapid temperature increases within the housing.
Another complication presented by sealed power distribution modules is the need to supply and distribute power from terminals which must pass from the exterior of the module to the interior of the housing, through the electronic circuitry, and back out to the exterior of the module. These power distribution terminals, therefore, must pass through the sealed housing, thereby potentially compromising the sealing integrity of the module. This potential is dramatically increased when the power distribution terminals take the form of bus bars which are flat plate-like terminals. Flat bus bars are desirable because of their effectiveness in reducing power dissipation. However, these bus bars are difficult to seal using traditional O-ring seals because the O-ring tends not to seal at edges of the bus bar but, rather, creates an xe2x80x9ceyeingxe2x80x9d effect which does not completely seal all surfaces of the bus bar.
Accordingly, a power distribution module is needed which provides power distribution bus bars with reduced power dissipation and reliable environmental sealing to resist ingress of liquids and other contaminants while minimizing the negative effects caused by the levels of heat associated with power distribution modules.
An environmentally sealed power distribution module is provided having a power distribution panel captured between a base housing and a top housing. The power distribution panel has bus bars which project from the base housing and the top housing. An o-ring type seal is disposed along a common perimeter between the base housing and the top housing and a gel type seal is disposed around the bus bars.
In an alternative embodiment, an environmentally sealed electronic module is provided having a circuit board disposed between a base housing and a top housing. The base housing and the top housing define an interface about a perimeter around the circuit board. Bus bars extend from the circuit board and project through the interface. An o-ring type seal is disposed within the interface and a gel type seal is disposed within the interface and around the bus bars.
In another alternative embodiment, an environmentally sealed module is provided having a base housing and a top housing attached at an interface. An electronic module is disposed between the base housing and the top housing. An o-ring type seal is disposed around the electronic module within the interface and has an open segment between free ends of the o-ring type seal. A gel type seal is disposed within the interface in the open segment and at least one terminal of the electronic module passes through the gel type seal.
In yet another embodiment of the invention, a hybrid peripheral seal is provided for sealing an interface. The hybrid peripheral seal comprises an o-ring type seal having an open segment between two free ends and a gel type seal disposed in the open segment.